This application is based upon and claims priority from Korean Patent Application No. 01-63948 filed Oct. 17, 2001, the contents of which are incorporated by reference.
1. Field of the Invention
The present invention relates to a method of precisely estimating the effective full-discharge capacity of a secondary battery which decreases in proportion to the degradation of the secondary battery.
2. Description of the Related Art
Secondary batteries are widely used in portable electronic apparatus, such as laptop computers, mobile phones, and camcorders. The charge and discharge states of such a secondary battery can be precisely monitored by determining the relative charging rate, which decreases in proportion to the degradation of the secondary battery. Precise data must be used to monitor and control the charge and discharge states of a secondary battery. Conventionally, this data is produced by periodically estimating and updating effective discharging capacity of the secondary battery.
In the conventional method of estimating effective full-discharging capacity of a secondary battery, which decreases in proportion to the degradation of the battery, only the number of charges and discharges of the battery are counted. Effective full-discharge capacity is estimated to be inversely proportional to the number of times the secondary battery has been charged and discharged. Conventionally, users charge secondary batteries that are partially discharged, i.e., from various different charge states, lowering the precision of the estimation of the full-discharging capacity of the secondary battery. The consequent imprecise estimation of the effective full-discharge capacity prevents precise monitoring of the charge state of the secondary battery, causing inconvenience in use of the battery.
To solve the above-described problems, it is an object of the present invention to provide a method of precisely estimating the effective full-discharge capacity of a secondary battery independent of the charging and discharging styles of users.
A method according to the invention includes sequentially fully charging a reference secondary battery and fully discharging the reference secondary battery until the reference secondary battery is dead, n times, and simultaneously measuring (i) a constant-voltage period in which the voltage of the reference secondary battery is essentially constant each time the reference secondary battery is fully charged and (ii) full discharge capacity of the reference secondary battery each time the reference secondary battery is fully charged, and storing the constant-voltage periods and corresponding full-discharge capacities measured; and measuring the constant-voltage period each time a secondary battery, essentially identical to the reference secondary battery, is charged, searching the constant-voltage periods stored for the reference secondary battery for the full-discharge capacity corresponding to the constant-voltage period measured for the secondary battery, and setting, for the secondary battery, as an effective full-discharge capacity, the full-discharge capacity of the reference secondary battery stored and corresponding to the constant-voltage period of the secondary battery that has been measured.
Preferably, the secondary battery is packaged with a microcomputer and the method includes searching the constant voltage periods stored for the reference secondary battery and setting the effective full-discharge capacity of the secondary battery with the microcomputer.
One application of the method includes, in setting the effective full-discharge capacity of the secondary battery upon charging of the secondary battery starting an internal timer when voltage of the secondary battery reaches an upper limit voltage indicating beginning of a constant-voltage period; stopping the internal timer when charging current supplied to the secondary battery declines to a lower limit current; and searching the constant-voltage periods of the reference secondary battery stored to obtain the full-discharge capacity corresponding to an elapsed time measured by the internal timer as a constant-voltage period, and setting the effective full-discharge capacity of the secondary battery to the full-discharge capacity of the reference secondary battery corresponding to the constant-voltage period measured as elapsed time by the internal timer.